The present invention relates to an indexable insert primarily intended for turning.
In connection with all turning operations a certain correlation exists between feeding and nose radius, the latter constituting the transition between the main cutting edge and the secondary cutting edge of the insert. Thus, in connection with rough machining the largest possible nose radius should be chosen in order to achieve a strong cutting edge. On the other hand a too large nose radius may cause vibrations. Therefore, in connection with fine turning a smaller nose radius is usually selected, normally always smaller than 2 mm. The disadvantage in connection with a small nose radius is that it increases the rate of wear of the insert and thus decreases the tool-life and the performance. The achieved surface finish of the workpiece is affected of the correlation between nose radius and feeding.
The entering angle is defined as the angle between the main cutting edge and the feeding direction. This angle has a considerable influence upon the mutual relationship between the different component vectors of the cutting forces and hence also upon surface finish and dimensional accuracy. The angle of tool back clearance is the angle between the secondary cutting edge and the feeding direction and it has an influence upon the smoothness of the turned surface. It is obvious that for a given insert the entering angle may not be changed without simultaneously changing the relief angle. Thus the surface finish and the dimensional accuracy are to a high degree sensitive to changes of the entering angle.
A permanent problem in connection with turning operations is that the desired surface finish is not achieved. Sometimes the surface finish may be improved by using a higher cutting speed and neutral or positive rake angles. However, the sensitivity to the adjustment of the entering angle still remains.
Round inserts may often manage a number of profiling operations from fine machining to rough machining. Said inserts usually have the shape of a truncated cone in order to allow sufficient clearance below the edge. For this reason said inserts are normally single-sided. Usually the round inserts generate a fine surface also in connection with high feeding since the round edge functions as a wiper, however the chip control may easily become deficient, especially in connection with small cutting depths when relatively wide and thin chips are formed that could be hard to break. Thereby long curled chips are formed that at worst may entangle around the insert holder and scratch the generated surface and possibly cause chip breakdown. Further they are afflicted with the inherent disadvantage that it is not possible to select an entering angle at a certain cutting depth since the insert is round. As an example of round inserts reference is made to U.S. Pat. No. 4,606 678.
A primary object of the present invention is thus to improve the deficient chip control that often is present in connection with round inserts, however the surface finish is maintained.